The present invention relates to flexible containers for filling, transport and storage of bulk material, Such containers can be made from flat-woven or round-woven base material, and the container bottom is formed for at least four paired, preferably equally large, flaps which are direct extensions of the container side walls. When the base material is joined together, at least one integrated lifting-loop can be made at the same time.
Containers, also called intermediate bulk containers, of the above mentioned type have been used for some time and have proved to be suitable for several purposes. An inner liner of impervious material is often used in use a container, and when they are to be filled with free-flowing bulk material, the container and the liner are usually first inflated by air. In Norwegian Pat. No. 138.134 (corresponding to U.S. Pat. No. 4,136,723 shows such a container having a double bottom. It is preferably equipped with two integrated lifting-loops having a total width substantially equal to half the circumference of the container such that the lifting-loops comprise all the longitudinal fibers of the container. The container can be filled by using an apparatus described in British Pat. No. 1,505,583 and it is then standing on a base without any extra support. Its lifting-loops can also be placed on a hook or the like before the container is inflated and filled with bulk material. The container can be made ready for further transport after filling. This can comprise closing the liner and gathering the lifting-loops together such that a suitable loop is formed and which easily can be placed on a hook or similar ligting device by pressing the lifting-loops together and securing them in this position. Before filling of bulk material, the container can be equipped with a permanent lifting grip.
However, it was found that inflating the container before filling at the filling station, especially when dusty bulk material should be filled, had some disadvantages as the air has to be displaced by the bulk material. The air which is pressed out will then contain dust from the bulk material and pollute the environment around the filling apparatus. When the bulk material is dusty, one must therefore use a dust removing device on the filling pipe, and the air sucked away is led to a dust filter for cleaning the air. Such a dust removing device complicates the filling apparatus and can hardly be made efficient without reducing the filling capacity of the apparatus. The fact that filling apparatuses having dust removing devices are not available everywhere where filling of such containers with dusty bulk materials will take place has accordingly limited the use of these containers.
It is known that containers having a central lashing knot in the bottom can be filled with fluidizable, dusty bulk material without preliminary inflation by hanging the container by its lifting-loops on a hook before filling. The central positioning of the lashing knot on such containers automatically ensures that the bulk material during the start of the filling is placed centrally at the container bottom and then gradually fills the container evenly all the way up without making the container lopsided.
If one tries to fill a container as described in the above Norwegian patent in the same way, i.e. without preliminary inflation with air, one will in some cases succeed, but in other cases the container bottom will be filled unevenly such that the whole container becomes lopsided. A further problem, especially with fluidizable bulk material, is that the inner liner will be pressed out between the bottom flaps into the double bottom.
However, because of the good experience with containers having integrated lifting-loops, it is desirable to continue with such a container construction, but to shape the container such that it would not have to be inflated at the filling station before it is filled with bulk material. Even though containers having a central lashing knot in the bottom are well suited for substantially dust-free filling of fluidized, dusty bulk material, without preliminary inflation at the filling station, when hanging by their lifting loops on a hook, they also have certain disadvantages.
During discharge of such containers, which normally is made by cutting the bottom by a knife or the like, the following can occur:
(a) The whole lashing knot will leave with the bulk material.
(b) A relatively large amount of fibers from the container will leave with the bulk material and pollute it because of the large concentration of container material or cloth which is present in the central part of the bottom.
(c) There are formed pockets on the outside of the lashing knot if it is not cut, completely out such that a complete discharge of the container must be made manually.